1. Field of the Invention
The present invention relates to an overcurrent detection circuit and overcurrent detection method, and more particularly, to an overcurrent detection circuit and overcurrent detection method adjusting current limit level when the temperature and a system voltage vary.
2. Description of the Prior Art
A traditional overcurrent detection circuit measures a load current outputted by a power converter, and transfers the load current to an overcurrent signal to determine whether the load current is greater than a reference signal to activate an overcurrent protection circuit, so as to protect a power system from excess current damaging the power converter or the load. In general, the reference signal is commonly to be a stable reference signal, which has a zero temperature coefficient or has an isolated power source, in other words, the reference signal has a constant value no matter the temperature or a system voltage in the power system varies.
However, the stable reference signal may not accurately respond to an occurrence of overcurrent in the power system. For example, please refer to FIG. 1A and FIG. 1B that are schematic diagrams of current limit levels (herein after CLL) of a traditional power integrated circuit (IC) when the temperature and a system voltage PVDD vary, respectively. As shown in FIG. 1A, when the temperature varies from a high temperature to a low temperature, the CLL increases from a low current to a high current. The CLL increases when the system voltage PVDD varies from a low voltage to a high voltage. Similarly, as shown in FIG. 1B, the lower the temperature and the higher the system voltage is, the higher the CLL becomes. In contrast, the higher the temperature and the lower the system voltage is, the lower the CLL becomes. If during a period of low temperature and high voltage, the overcurrent detection circuit may activate the overcurrent protection circuit to drain the overcurrent earlier than the load current reaching the CLL, which may lower a power efficiency of the power IC. If in the high temperature and the low voltage situation, the overcurrent detection circuit may activate the overcurrent protection circuit after the load current has reached the CLL, which may lead to the overcurrent protection circuit not draining the overcurrent in time, and risking damage to the power system or the load.
As can be seen, the CLL is deeply influenced by the temperature and the system voltage, which may lead to the stable reference signal not accurately responding to an occurrence of overcurrent in the power system. Thus, there is a need to improve the prior art to avoid a judgment failure of the overcurrent.